cleaned out boilerplate migration imports that arent actually used

 - Legacy-Id: 8709

Author: rjsparks

ietf/group/migrations/0008_materials_managers.py

@@ -1,8 +1,5 @@
 # -*- coding: utf-8 -*-
-from south.utils import datetime_utils as datetime
-from south.db import db
 from south.v2 import DataMigration
-from django.db import models
 
 class Migration(DataMigration):